The present invention relates in general to an infrared sensor device and in particular to a handheld or headgear mountable infrared sensor device capable of displaying fused or mixed radiation from infrared and other spectral sensors.
As is well known, light absorption properties of the atmosphere define several frequency bands that are favorable to the transmission of light without undue absorption. Some of these frequency bands define spectral ranges that provide useful information for aiding in certain aspects of night vision. Generally, these spectral ranges may be described as the visible (VIS) band (approximately 0.4 μm-0.76 μm), the near infrared (NIR) band (approximately 0.76 μm-1.1 μm), the short wave infrared (SWIR) band (approximately 1.1 μm-3 μm), the medium wave infrared (MWIR) band (approximately 3 μm-7 μm), and the long wave infrared (LWIR) band (approximately 7 μm-18 μm). The VIS, NIR and SWIR bands are dominated by reflected light such as starlight. The LWIR band is dominated by emitted light, or thermal energy. The MWIR band has both reflected and emitted radiation, and exhibits approximately equal parts of reflected light and emitted light during the day.
Infrared sensors are devices sensitive to radiation in a limited speciral range of infrared radiation, typically from one of the NIR, SWIR, MWIR or LWIR bands. Such sensors have been used for night vision applications. However, none of the prior night vision systems provide satisfactory performance for field use under harsh environmental conditions. For example, one infrared device utilizes an LWIR sensor and a display screen to detect and display thermal energy. However, the LWIR sensor requires cryogenic cooling. This is required to maintain the sensor at a stable and high quantum efficiency. Otherwise, the display is distorted by temperature fluctuations of the sensor itself. Cooling adds substantial cost and bulk to the LWIR sensor thus limiting the applications where cryogenically equipped LWIR sensors may be used. Yet other night vision systems employ NIR sensors, such as an image intensifier (I2). Although the resolution of I2 is much better than LWIR, it does not function is well as the LWIR sensor in harsh environmental conditions such as in fog, haze, smoke, and complete darkness.
Therefore, there is a need for an infrared sensor system that produces a good resolution image, and is adaptable for use in harsh environments.
Further, there is a need for an infrared sensor system that take the advantages of both sensors and overcome the shortcomings of both sensors.